This invention relates to a method and apparatus for feeding an extrudable fuel into a pressurized combustion chamber in such a manner that an elevated pressure is maintained in the combustion chamber, and that fuel is introduced into the chamber at a constant, controllable rate. More particularly, this invention relates to using an extruder having an outlet opening of reduced cross-sectional area relative to the area of the extruder, to transport the fuel to the combustion chamber and to compact fuel particles at the point of introduction into the chamber. The compacted fuel is used to provide a pressure seal for the chamber, and is re-dispersed into particles by an atomizing means, as the fuel is introduced into the chamber.
With the recent advances in coal beneficiation and micronization, the concept of using coal in direct-fired gas turbine combustors has become more attractive. One of the major problems associated with such a combustor is that coal, being a solid, is difficult to feed in a controlled manner into a pressurized combustor. One method that has been proposed for feeding coal into the combustor is to slurry the coal and introduce it as a liquid. However, there are certain problems which must be considered for a slurry feeding system, including slurry stability, combustion stability, ignition delay, particle agglomeration, the need for water quality control, and the loss of combustion efficiency resulting from high water content required to form the slurry. A dry or near-dry coal feeding method avoids many of these problems and results in higher combustion engine efficiency.
Previous investigators have employed a dry feed concept in direct-fired, coal-burning gas turbine combustors. Two significant problems which have been prevalent in these previous systems are fluctuating fuel flow rates and flow "pulsations" associated with gear-type coal pumps. Modern gas turbine combustors are sophisticated systems requiring accurate fuel flow control. Additionally, some pressurized combustors exhibit significant sensitivity to combustor pulsations.
Furthermore, a number of systems have been employed in the past for extruding coal in various situations. However, prior art coal extrusion systems have not been directed to the problem of feeding coal to a pressurized combustion chamber at a continuous, controllable rate so as to provide stable combustion, and in such a manner that the temperature and pressure in the combustor are maintainable at desired levels for a particular load condition. Also, conventional coal extrusion systems are directed to processes using much larger coal particle sizes than are employed in gas turbine systems.
Accordingly, it is seen that it is an object of the present invention to provide a method for feeding a dry, extrudable fuel to a pressurized combustion chamber at a controllable rate.
It is a further object of the present invention to provide a method for feeding coal into a pressurized combustion chamber so as to provide stable combustion, and so that the temperature and pressure in the chamber are maintainable at a constant, controllable level for a fixed load condition.
It is also an object of the present invention to provide a method for feeding finely ground coal particles into a gas turbine combustor.
It is still another object of the present invention to provide an apparatus for feeding an extrudable fuel into a pressurized combustion chamber at a controllable rate, so that direct firing of the fuel results in stable combustion in the chamber.